518 Reproduction in Fresh- Water Alge.  [September, 
jelly. After they have entered the water the old portions of 
the thread become endowed with motion, like the oscillatorex, 
and their exit is apparently caused by this movement. The 
roundish cells of the filaments now grow transversely, that is, 
- vertically, to the axis of the filament, become disk-like, and then 
divide, the division planes being parallel to the axis of the old 
filament, which now consists of a series of short threads, the 
axis of whose growth is vertical to its own. The numerous 
threads which are thus formed continue to elongate and to in- 
crease the number of their cells ; they then curve, place their two 
terminal cells in contact with those of the next row, and thus the 
whole unite into a single curved Nostoc-filament. Individual 
cells, apparently without any definite law, become heterocysts. 
In the mean time the gelatinous envelope of the new filament is 
developed, and the original microscopic substance attains or even 
exceeds the size of a walnut by continuous increase of the jelly 
and division of the cells.” 
In the Conferve family reproduction is effected by means of 
motile asexual bodies called zodspores. The members of the 
genus Cladophora, a portion of one of which is highly magnified 
in Figure 89, are quite common, deep green, irregularly branched 
alge. When these zodspores are to form 
the protoplasmic contents of certain cells 
contract into oval masses, each of which 
upon its escape through the broken cell-wall 
moves away in the water by means of two 
vibratile cilia which are attached to one end 
of the spore. This rotary and progressive 
motion lasts for some time, after which the 
body comes to rest, loses its cilia, and, at- 
taching itself to some support, germinates 
and produces a new Cladophora. There are 
frequently two distinct sizes of these 'asex- 
ual spores produced in separate cells of the 
same plant, as seen in the figure ; the large 
ones are called macrozodspores, and the 
small ones microzodspores. It has been 
which 
_ (Fte. 89.) CLADOPHORA. 
stated by Pringsheim that the microzoöspores conjugate, in 
case we would have sexual action taking place between ase 
spores. It is certainly quite interesting to see these little animal- 
like bodies moving rapidly around inside the mother cell, as w° 
as darting away upon making their exit. Sometimes two oF more 
